Methods for relieving stresses in and straightening tubular workpieces



M y 1962 G. H. APPEL 3,035,340

METHODS FOR RELIEIVING STRESSES IN AND STRAIGHTENING TUBULAR WORKPIECES Filed April 25, 1958 5 Sheets-Sheet 1 r -ca M I I I I i I I I I I I II I I I I: I I i I I:

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GERHARD H. APPEL BY walvu ATTORNEYS May 22, 1962 APPEL 3,035,340

G. H. METHODS FOR RELIEVING STRESSES IN AND STRAIGHTENING TUBULAR WORKPIECES Filed April 25, 1958 5 Sheets-Sheet 2 INVENTOR.

GERHARD H. APPEL mam ATTORNEYS M y 1962 G H APPEL 3,035,340

METHODS FOR RELIE'VING STRESSES IN AND STRAIGHTENING TUBULAR WORKPIECES Filed April 25, 1958 5 Sheets-Sheet 3 3 5 a Q a g l N N I g v 8 8 am! l Ix Q1 1 x 8 1' \J m g P 1 1 :s INVENTOR.

GERHARD H. APPEL ATTORNEYS May 22, 1962 APPSEFL 3,035,340

G. H METHODS FOR R EV RESSES IN AND STRAIGHTENI TU AR WORKPIECES Filed April 25, 1958 5 Sheets-Sheet 4 I. FEED- DIES OPEN- NO STRESS STRESSDIAGRA" l llllllllllllilllIlllllllllllllilll 1E. PLASTICIZING I v 1 I l INVENTOR.

GERHARD H. AP'PEL May 22, 1962 G. H. APPEL 3,035,340

METHODS FOR RELIEVING STRESSES IN AND STRAIGHTENING TUBULAR WORKPIECES Filed April 25, 1958 5 Sheets-Sheet 5 1. FEED DIES OPEN FEED | n i c B A STRESS DIAQRAM I I LLLLLLLLL Illlllllllllll||ll|||||||||| II. DIES CLOSED- NOT YET PLASTICIZED I lllllllllllllllllllllllll| III. PLASTICIZING |-o c i B A STRESS DIAGRAM III I l I l lll llllllllilll INVENTOR.

GERHARD H. APPEL ATTORNEYS United rates 3,035,340 ME'EHUDS FOR RELIEVING STREESES IN AND STRAIGHTENING TUBULAR WORKPIECES Gerhard H. Appel, Belle River, Gntario, Canada, assignor to Appel Process, Ltd, (lshawa, Ontario, Canada Filed Apr. 25, 1958, Ser. No. 730,850 6 Claims. (Cl. 29--544) This application relates to methods for forming and straightening and relieving stresses in tubular workpieces.

US. Patent No. 2,986,051 of May 30, 196 1, discloses a machine for forming workpieces characterized by the fact that the workpiece feed is incremental and intermittent and in off-beat relation to the movement of dies radially and transversely of the workpiece feed axis for forming the workpiece. The dies and the feed means move in offbeat relation so that the dies form the increments positioned within their throat while no feed takes place, and feeding takes place between forming movements of the dies, and die movements towards the workpiece axis take place between incremental feeding strokes.

That Patent No. 2,986,051 also discloses the use of a mandrel within the workpiece and coaxial with the throat when the workpiece is a tube to be formed on a mandrel.

in still another U.S. Patent No. 2,894,421 of July 14, 1959, I disclose a feed means for feeding a workpiece to and through the throat of the dies, such feeding means including a chuck which holds the workpiece and is positioned a substantial distance behind the throat of the dies with the chuck moving on rails of the machine in properly guided relation, so that the axis of feed is the same as the mandrel axis and the throat axis.

That Patent No. 2,894,421 also discloses an apparatus which is arranged to cooperate with a workpiece and receive and hold and guide its leading end as it passes from the throat of the dies at one point ahead of the throat of the dies in "a manner to hold the workpiece increment that has already been formed in the throat and at that time relieved of stresses, holding such increment while another increment of the workpiece behind the first named increment is being formed in the throat of the dies and there relieved of stresses.

in this application, I disclose a means, particularly adapted for tubular workpieces, which supports the leading portion of a tubular workpiece as it emerges from the throat of the dies at two longitudinally spaced points ahead of the throat of the dies. These supporting means, positioned ahead of the throat of the die at two points which are longitudinally spaced from each other and from the throat of the die, support and receive and hold increments of the workpiece emerging from the throat of the dies where they have been relieved of stresses as they are formed in the dies while following increments of the workpiece are being formed in the dies and there relieved of stresses.

Inasmuch as the machine in general and the feeding means in general are both disclosed with great clarity in the aforementioned patents and by this time are wellknown to those skilled in the art and inasmuch as the details of construction of such feeding means and of such machine in general form. no part per se of the present invention, the same will not be disclosed except to the extent necessary for a proper understanding of the invention as embodied in the device disclosed in the appended drawings described in the following specification.

In these drawings:

FIG. 1 is a longitudinal section view of a machine formed in accordance with the invention with two points of support ahead of the throat of the dies and longitudinally spaced from each other and from the dies throat, with the parts shown in a beginning stage of the forming operation.

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Patented May 22, 1932 FIGS. 2 and 3 are similar views but showing the parts in later stages of the forming operation.

FIGS. 4-5 are diagrammatic views.

Referring to the drawings, the apparatus shown is adapted to carry out the new straightening and stress relieving method in cooperation with a forming machine of the type disclosed in Patent No. 2,896,051. The machine comprises a die set 20 supported on a frame 21 which is part of the fixed structure of the machine. Such frame has fixed parallel rails 22 which support and guide a feeding chuck 23 for linear movement towards and from the dies. Any suitable drive means may be utilized for so moving the chuck. The chuck grips and supports one end of a workpiece such as the metal tube 26 and the chuck advances towards the dies to feed the workpiece axially through the throat 27 of these dies.

The dies move radially and transversely of the axis of feed of the workpiece 26 and their working faces which define throat 27 are shaped to form the work to any desired external contour, the forming operation being effected upon a mandrel 30 disposed within the tubular workpiece within the die throat. The mandrel may be supported in any well-known manner as for example by having a part 31 rearwardly extending through the chuck 23 and being supported on fixed structure of the machine at its rear end.

In operation, the chuck and the workpiece are advanced intermittently and in off-beat relation to the stroke of the dies to feed the workpiece axially through the die set. Between feeding strokes the dies are actuate-d to subject the increment of the workpiece within the die throat to the forces or loads on the dies, with all of the dies acting simultaneously on the entire area of the workpiece within the throat of the dies, the dies girdling the workpiece substantially completely for this purpose.

The die elements plasticize the material and force it into precise axial alignment with the throat. The longitudinal stresses within the increment of the workpiece in the throat are completely relieved when the material becomes plastic under the dies and as the increment formed within the dies leaves the throat of the dies that increment is relieved of stresses. It will be clear by now that if that increment can thereafter be maintained in strict axial alignment with the throat of the dies and the path of the chuck supporting the workpiece and feeding it, that increment will remain relieved of stresses, will remain straight and in proper alignment with the axes and throats of the chuck and dies as desired.

Accordingly, support means which specifically form the present invention have been provided and such will now be described.

The support means includes the following major elements. First, there is a fixed outer tube 40 supported from fixed structure 21 of the machine. Within this outer tube 46 is a slidable inner tube 42. formed so that a counterbore 41 at its trailing end receives the leading end 43 of the workpiece and further formed with a shoulder 44 near its leading end which cooperates with the interior surface 45 of the fixed tube 40 whereby the latter functions as a guide during the longitudinal movement of the inner tube 42 in response to forward movement of the leading end of the workpiece 26 as the latter is fed through the die throat.

The third element is an extension 48 of the mandrel 34 which projects forwardly from the die throat 27 a considerable distance and is provided with two longitudinally spaced shoulders or discs 5ll-52 well forward of the die throat. The extension 48 and consequently the shoulders 50, 52 are unitary with the mandrel 3i and its rearward extension 31 and hence the shoulders 59, 52 provide supports as well as guides for the inner tube 42 and likewise for the leading end of the workpiece 26 as the latter is fed well past the die throat 27 during the later stages of the forming operation of the long workpiece.

The function and operation of the parts just described is as follows:

Normally, the inner tube 42 is positioned as close as possible to the die throat 27 so as to receive and be engaged at 41 by the leading end 43 of the workpiece 26 as it emerges from the die throat. Thereupon, the leading end 43 of the workpiece moves forwardly and in so moving moves the inner tube forwardly, with the latter being guided in its movement by the shoulders 50, 52 of the mandrel extension 48 as well as by its own shoulder 44 guided by the inner surface 45 of the outer tube 40. Thereafter, the leading end of the workpiece reaches the first shoulder 50 of the mandrel extension 48 so as to be guided thereby and subsequently the leading end of the workpiece, after passing by the first shoulder reaches the second shoulder 52 of the mandrel extension so as to be guided by it. At this moment, the inner tube 42 has completed its function of supporting the leading end 43 of the workpiece. The inner tube soon reaches and passes beyond the forward open end of the fixed tube 40 of the machine whereupon the inner tube 42 may be removed from the leading end of the workpiece and thus from the machine and put to one side. Thereafter, the leading end of the workpiece advances beyond the leading end of the fixed tube 40 and onto conventional supports (not shown) outside the machine.

During all this time, and during the entire process following increments of the workpiece were being formed in the die throat and were at that time being relieved of stresses. Meanwhile, leading increments of the workpiece, after leaving the die throat wherein they were destressed were supported and guided in strict axial alignment with the die throat and the throat of the chuck, by part 41 of the inner tube 49 at first, and later by the shoulders 51 52 directly, these first having cooperated with the leading end of the workpiece through the inner tube but later cooperating directly with the leading end of the workpiece. As disclosed in Patent No. 2,894,421, counter-pressure means may be provided for yieldably resisting and controlling the advance of the inner tube 42 during the early part of the forming operation and such resistance means may take any desired form. For example, it may be provided by suitable pneumatic or hydraulic resistance means all well-known to the art and forming no part per se of the present invention.

Upon completion of the forming operation the dies are opened up to enable withdrawal of the work, the feeding means 23 are retracted in the usual manner and the machine is now ready for receiving once again the inner tube 42 which had previously been set aside and also for receiving another workpiece which is to be formed over its length upon the mandrel by means of the dies and which may be formed for any desired length within the feeding capacity of the machine.

The novel method hereof improves the product, delivering a finished tubular workpiece which is precisely straight and is completely free of longitudinal stresses and which are of a substantial degree of accuracy with respect to uniformity of thickness of the workpiece wall.

It is obvious that with the axis defined by the two shoulders, the die throat and the feeding chuck being a straight line, defined by the four points just mentioned, workpieces of great length may be delivered by the machine with the workpieces, despite their great length, being truly straight, quite nearly perfect as to uniformity of wall thickness, and with the increments of the workpiece once relieved of stresses in the forming die remaining relieved of longitudinal stresses.

In this application we have also disclosed diagrammatically the operation of the double support hereof as contrasted from the single support of my Patent No. 2,894,421.

FIG. 4 shows the single support operation diagrammatically through several parts of the movements of the dies and the workpiece, and FIG. 5 contrasts the foregoing with a similar view but disclosing the operation of the double support of this application.

In these drawings a tubular workpiece 26 is held at the right end in a feed chuck 23 and is supported at the left end by a single support 50 in FIG. 4 and double support 58, 52 in FIG. 5. Between the chuck and the support or supports as the case may be are the dies 20.

FIG. 4SINGLE SUPPORT (l) Now referring to FIG. 4, the single support diagram, we see that when the dies 20 are open the workpiece 26 which is rearly truly straight is bowed or curved, and in this case the curve is shown as an upward curve between the chuck 23 and the support 56 in parts A-B of the workpiece.

(ll) As the dies close, they transform the single bow in the workpiece, A and B, into two bows, B, between support 50 and dies 20, and A, between dies 29 and chuck 23. The stress diagram shows that now parts A and B are both under stress.

(ll) As the closed dies plasticize and the work increment within the dies throat is completed, the double bow A-B still remains and these parts A and B, though relieved of longitudinal stresses to a considerable extent, remain still under lateral stress, as shown in the stress diagram, though in a reduced amount, due to mass inertia.

As feed continues, the completed part C of the workpiece, beyond support 50 will deflect from the centerline and take a position at an angle to the centerline.

Hence, though a single support functions to a considerable extent to straighten the workpiece and to relieve stresses therein a described in Patent No. 2,894,421, nevertheless it does not completely prevent part C of the workpiece from leaving the centerline and feed axis and such part C of the workpiece takes an angle from the centerline as it emerges from the machine and some degree of inaccuracy of alignment and straightness of the workpiece results.

FIG. 5-DOUBLE SUPPORT On the other hand, when a double support is used as shown in FIG, 5, the parts C and D, that is to say, the part C between the two supports 50-52 and the part D beyond the support 52 not only are straight but also at all times remain in alignment with the feed axis and centerline of the chuck, the dies throat and the support.

(I) When the process starts, with the dies open, part A-B will be bowed upwardly and part C will likewise be bowed downwardly, but with its left end in the support 52, and the stresses in parts ABC will be as shown in the stress diagram.

(II) When the dies are closed, parts B and C will be displaced from the preceding position and will become straight and aligned with the feed axis and freed of stress, as shown in the stress diagram.

(Ill) When the dies are closed and plasticizing takes place, parts BC and D remain straight and aligned with the feed axis and destressed, as shown in the stress dia gram. When the dies open and the work increment completed, parts B, C and D will remain straight and aligned with the feed axis, and destressed.

Conclusion Hence, it is clear that a double support gives quite a diiferent result from a single support, namely the double support causes those parts of the workpiece beyond the first support to remain straight and aligned with the feed axis and destressed whereas in the case of a single support machine and method, the workpiece beyond the first support, regardless of what other characteristics it may possess, is not aligned with the feed axis but is deviated from it to some extent with resultant inaccuracies and distortions. These are prevented by the use of the double support machine and method of this application.

Now having described the machine hereof and the method hereof, reference should be had to the claims which follow:

I claim:

1. A method for cold forming an elongated, tubular metal workpiece on an internal mandrel, comprising simultaneously applying to the surface of a minute increment of the metal workpiece at least three, radially arranged, inwardly directed, equally spaced, equal and opposed pressures engaging and substantially completely girdling the workpiece; applying the pressures to the workpiece by at least three radially arranged pressure applying dies providing a die throat, with each die subjected to two opposing, equal, transverse forces, each of which transverse forces has a transverse component and a radial component, the transverse components being directed so that they are equal and opposite and thus balance themselves out, leaving only a net radial resultant directed along an extension of the radius of the workpiece and towards the central axis of the workpiece so that each force on a die which applies pressure to the workpiece is truly radial to the workpiece and has no unbalanced transverse components; the method further including axially push feeding the workpiece through the throat of the dies and engaging the leading end of the workpiece immediately as it emerges from the throat of the dies and holding and guiding such end thereafter in precise axial alinement with the axis of push-feed while the workpiece is push fed; supporting the workpiece on the mandrel therein not only as it passes through the dies but also immediately after it leaves the dies on two longitudinally spaced shoulders of the mandrel, both shoulders being a short distance forward of the dies, and of the internal diameter of the finished workpiece.

2. A method for cold forming an elongated, tubular metal workpiece on an internal mandrel, which method comprises applying to each of many longitudinal adjacent minute increments of a metal workpiece, in successive steps, so as to extend over substantially its entire exterior surface, at least three, radially arranged, inwardly directed, equally spaced, equal and opposed and simultaneously applied pressures engaging and substantially completely gridling the workpiece; applying the pressures to the workpiece by at least three radially arranged pressures applying dies providing a die throat with each die subjected to two opposing transverse forces, the two opposing transverse forces being so directed that their transverse components are equal and opposite and thus balance themselves out, leaving only a net radial resultant of the two forces, so that each force on a die which applies pressure to the workpiece becomes truly radial and has no unbalanced transverse components, and so that the pressures on the workpiece applied by each pressure applying die are balanced out by equal and opposite pressures applied by the remaining pressure applying dies; the method further including axially push feeding the workpiece through the die throat of the dies and engaging the leading end of the workpiece immediately as it emerges from the throat of the dies and holding and guiding such end thereafter in precise axial alinement with the axis of pushfeed while the workpiece is push fed; supporting the workpiece on the mandrel therein not only as it passes through the dies but also immediately after it leaves the dies on two longitudinally spaced shoulders of the mandrel, both shoulders being a short distance forward of the dies, and of the internal diameter of the finished workpiece.

3. A method for cold forming an elongated, tubular metal workpiece, having a central axis on an internal mandrel, comprising the steps of surrounding substantially the entire outer peripheral surface of a single axial increment of the workpiece with at least three opposed dies providing a die throat, each die arranged radial to the workpiece central axis; simultaneously loading all of the dies by subjecting each of them to two equal and opposing forces which are transverse relative to the die axis and which are so arranged as to balance out all transverse components of said two opposing forces and leave only a radial resultant which radial resultant is directed towards the workpiece central axis along the die axis; whereby the resultant load on each die is radial and has no unbalanced transverse components, and with the said radial resultant on each die being equal to the radial resultant of every other die; moving the dies under the influence of their respective radial resultant loads into engagement with the workpiece increment for transmitting the respective resultant loads to the workpiece and thereby applying pressure to the workpiece for forming it; the method further including axially push feeding the workpiece through the throat of the dies and engaging the leading end of the workpiece and holding and guiding such end thereafter in precise axial alinement with the axis of push-feed while the workpiece is push fed; supporting the workpiece on the mandrel therein not only as it passes through the dies but also immediately after it leaves the dies on two longitudinally spaced shoulders of the mandrel, both shoulders being a short distance forward of the dies, and of the internal diameter of the finished workpiece.

4. A method for cold forming a tubular metal workpiece, which is elongated and rod-like in shape and thus has an elongated central axis on an internal mandrel, said method employing at least three pressure applying dies which are equally spaced on workpiece radii circumferentially around the periphery of the workpiece in a plane normal to its axis and which dies girdle the workpiece and are movable towards and away from the axis, said dies providing a die throat, said method further comprising repeated identical cycles of steps with each cycle including the dies engaging and acting on a small axial increment of the workpiece and with each cycle comprising the steps of gradually and simultaneously moving all of the dies equal minute distances inwardly towards the workpiece axis inwardly of the workpiece surface and under equal loads whereby the dies gradually squeeze the workpiece increment then worked upon until the metal in that workpiece increment flows and the periphery of that workpiece increment assumes the shape of the die faces engaging the workpiece; then stopping the inward movement of the dies and holding the die loads for a short time; and then retracting the dies away from the workpiece axis; and then moving the workpiece axially through the dies to present a succeeding increment of the workpiece to the dies; and repeating the cycles until all increments of the workpiece from one end to the other have been successively engaged and formed by the dies; applying the pressures to the work piece by subjecting each of the dies to two opposing transverse forces each of which forces have transverse components and radial components and with their transverse components being so directed that they are equal and opposite and balance themselves out leaving only a net radial resultant so that each force on each of the dies, which applies pressure to the workpiece, is truly radial and has no net or unbalanced transverse components; the method further including axially push feeding the workpiece through the thoat of the dies and engaging the leading end of the workpiece and holding and guiding such end thereafter in precise axial alinement with the axis of push-feed while the workpiece is push fed; supporting the workpiece on the mandrel therein not only as it passes through the dies but also immediately after it leaves the dies on two longitudinally spaced shoulders of the mandrel, both shoulders being a short distance forward of the dies, and of the internal diameter of the finished workpiece.

5. A method for cold forming an elongated tubular metal workpiece, having a central axis, on an internal mandrel, comprising numerous identical cycles of steps, with each successive cycle acting upon a successive single axis increment of the workpiece, each cycle comprising essentially the steps of surrounding substantially the entire outer peripheral surface of a single axial increment of the workpiece, with at least three opposed pressure applying dies which are arranged radially relative to the workpiece axis to provide a die throat; simultaneously loading all of the dies and moving them under the infiuence of their loads towards and into pressure applying engagement with the workpiece, with the movement of each of said dies being only in the direction of a single radius of the workpiece, with the load on each of the dies being formed of a radially directed resultant force directed only in the same direction as the respective single radius which defines the direction of movement of that die and also being formed of pairs of non-radial force components with each non-radial force component of each pair being equal to and oppositeto and counter-i balancing and cancelling out the other non-radial force component of that pair and with the radially directed resultant forces of each of the dies being equal to one another; holding the dies in a pressure applying engagement with the workpiece for a pre-determined time for forming the workpiece increment; then releasing the loads simultaneously and retracting the dies from the workpiece along the same path in which they moved towards the workpiece; the method further including axially push feeding the workpiece through the throat of the dies and engaging the leading end of the workpiece and holding and guiding such end thereafter in precise axial alinernent wth the axis of push-feed while the workpiece is push fed; supporting the workpiece on the mandrel therein not only as it passes through the dies but also immediately after it leaves the dies on two longitudinally spaced shoulders of the mandrel, both shoulders being a short distance forward of the dies, and of the internal diameter of the finished workpiece.

6. A method for cold forming a tubular metal workpiece having a central axis, on an internal mandrel, comprising loading substantially the entire outer periphery of a single increment of the workpiece with forces that are inwardly directed and which resolve into force components which are either radial to the workpiece axis or are normal to radii of the workpiece and tangent to a hypothetical circle whose axis is th axis of the workpiece; and with all of the radial force components being in balance at the axis of the workpiece and with each of said normal force components being balanced by another equal and opposite normal force component; there being no forces at any time which do not resolve into truly radial components or normal-to-radii components; said loading being characterized by being rapidly applied and removed in a uniform time pattern; applying the loading to successive increments of the workpiece; and changing the increments upon which the loading is applied during the load removed time of the loading time pattern; the method further including axially push feeding the workpiece through a throat of dies which provide the forces and engaging the leading end of the workpiece immediately as it emerges from the throat of the dies and holding and guiding such end thereafter in precise axial alignment with the axis of push-feed while the workpiece is push fed; supporting the workpiece on the mandrel therein not only as it passes through the dies but also immediately after it leaves the dies on two longitudinally spaced shoulders of the mandrel, both shoulders being a short distance forward of the dies, and of the internal diameter of the finished workpiece.

References Cited in the file of this patent UNITED STATES PATENTS 1,319,837 Brinkman Oct. 28, 1919 1,319,838 Brinkman Oct. 28, 1919 2,114,302 Harter Apr. 19, 1938 2,178,141 Frame Oct. 31, 1939 2,197,391 Biggert Apr. 16, 1940 2,247,863 Tiedmann July 1, 1941 2,595,319 Woldman et al. May 6, 1952 

